1. Field of the Invention
This invention relates to data center migration, and more specifically to a platform for migrating computer mainframe applications and volumes of data from a source Direct Access Storage Device (DASD) to a remote target DASD.
2. Related Art
Businesses that offer technology, such as telecommunications, must deal with the necessity of collecting, storing, and managing large volumes of data on a daily basis. It is common for such companies to utilize several mainframe computers located in various facilities known as data centers.
These data centers are strategically placed in geographical locations, taking into consideration such aspects as data network topology, user proximity, local real estate markets and economy, local employment base, and survivability of natural disasters. Often, strategic direction requires a company to move a data center from one location to another, which consists of moving all data of a source mainframe to another remote target mainframe. Data to be moved includes system configuration, operating system, applications, support, and user data. Sometimes an entire mainframe is to be moved, while other situations dictate that only certain applications be moved.
In essence, moving a mainframe from one location to another consists of migrating data from a source Direct Access Storage Device (DASD) to a target DASD. These DASD units are physical devices used for permanent storage on mainframe computers. They store all data that are used by a mainframe computer, and, thus all data that must be moved as part of a data center migration. Therefore, a data center migration is essentially a migration of data from one DASD to another.
Migrating such large volumes of data requires several provisions to minimize business impact. Some aspects that must be considered are:
(i) Data integrity: Moving large volumes of mission-critical data exposes the business to data corruption. In addition to exposures due to the physical transfer of data, updates and changes made to data during the move may not be reflected at the target location;
(ii) Minimal application downtime: A business cannot be put on hold for the extended periods of time required for traditional data migrations. Minimizing application downtime during the move is critical for the users of the data center;
(iii) Cost: The cost of resources needed for a data center migration is a fundamental business concern. Minimizing the cost of resources such as data center equipment, transportation vehicle, and data transfer network is essential;
(iv) Manpower: People resources represent another cost of a data center migration. Minimizing the headcount needed is always a concern; and
(v) Time: Reducing the amount of time needed for a data center migration reduces such liabilities as resource/manpower costs, application downtime, and data integrity exposures.
There are three (3) traditional methods of data center migration: Tape Backup and Ship, Tape Drive Channel Extension, and Physically Moving DASD Units.
a. Tape Backup and Ship
The Tape Backup and Ship method consists of backing up to tape all data on the source DASD. This is also known as tape dump-and-restore. All data on the source DASD are downloaded to magnetic tapes. The tapes are then shipped by truck, rail, or air to the site of the target DASD. When received, the tapes are loaded onto the tape drive of the target mainframe and all data are uploaded to the target DASD.
This method obviously requires a large number of magnetic tapes. For every one gigabyte (G.B.) of data to be migrated, approximately two (2) tapes are needed. This means for a typical migration of 2500 G.B., 5000 magnetic tapes are required.
Another major disadvantage of this method is the fact that customer applications must be down for the entire time it takes to download the data to tape, ship the tapes, and then upload the data to the target DASD. Table 1 below shows the approximate time (in minutes) it takes to backup data from a source DASD to tape, transport the tapes, and then restore the data to a target DASD. Time is indicated as a function of gigabytes to be migrated, and assumes eight (8) tape drives are used. An estimate of twelve (12) hours is used for transport time, assuming cross country air freight is used.
One important disadvantage of this method is that all customer applications are inaccessible during this time. For example, during the migration of a data center consisting of 1000 G.B. using the Tape Backup and Ship method, all applications are down for approximately 3.28 days.
Another disadvantage of this method is the resources and associated costs needed to conduct the migration. Extra manpower is needed to perform the tape download and upload, and to physically move the tapes. Transportation of the tapes may incur significant costs, especially if it is over great distances and requires expedited delivery. Also, as indicated in Table 1 above, the cost of tapes may be high if a large amount of data is to be migrated.
Another disadvantage of this method is its exposure to data corruption. Due to the fact that the tapes serve as an intermediate medium, data may be corrupted during the downloading or uploading of data to and from the tapes. There also exists the possibility of tapes being lost or damaged during transportation and many exchanges of hands, or at least of tapes being placed out of sequence. Finally, unplanned application updates that are made during or after the source DASD download may not be reflected at the target DASD.
b. Tape Drive Channel Extension
The Tape Drive Channel Extension method consists of connecting a channel extender unit to the source mainframe tape backup system. The source mainframe treats the channel extender as a tape drive and writes data to the extender as data is being read from the source DASD. The channel extender unit then sends this data over a DS-3 Data Link connected to the target tape drive which writes the data to tapes at the target data center. The tapes must then be manually uploaded to the target DASD.
As with the Tape Backup and Ship method, this method obviously requires a large number of magnetic tapes. For every one (1) gigabyte (G.B.) of data to be migrated, approximately two (2) tapes are needed. This means for a typical migration of 2500 G.B., 5000 magnetic tapes are required.
Also as with the Tape Backup and Ship method, customers applications must be down and inaccessible for a significant period of time. Applications must be down during the backup (source mainframe writes DASD data to a channel extender unit,) and restore (tapes are uploaded to a target DASD) processes. However, there is no tape transport time needed, and the restore process may begin approximately one (1) hour after the backup process begins. Table 2 below shows the approximate time (in minutes) it takes to backup data at the source data center, and to restore data at the target data center. Time is indicated as a function of gigabytes to be migrated, and assumes eight (8) tape drives are used.
As with the Tape Backup and Ship method, all customer applications are inaccessible during this time.
Another disadvantage of this method is the resources and associated costs needed to conduct the migration. Extra manpower is needed to perform the restore process at the target site. Also, as indicated in Table 2 above, the cost of tapes can be high if a large amount of data is migrated.
Finally, due to the fact that both tapes and channel extender units are serving as intermediate media, data may be corrupted during the backup or restore processes. Also, unplanned application updates that are made during or after the backup process may not be reflected at the target site.
c. Phsically Moving DASD Units
Physically Moving DASD Units consists of dismantling, transporting, and re-installing the source DASD units at the target data center.
The obvious disadvantage of this method is the exposure to physical damage that the DASD units have during the transportation process. This also comprises an exposure to data corruption if physical damage is incurred.
Another disadvantage of this method is that customer applications must be down for the entire time it takes to dismantle, transport, and re-install the DASD units. This time varies with the amount of available manpower and transportation resources.
Another disadvantage of this method is the cost of transportation and manpower needed to dismantle, transport, and re-install the DASD units.
In addition to the three (3) methods of data migration discussed above, there is product currently on the market that is used for a data center migration: Sterling Software""s Network Data Mover (NDM). NDM is a mainframe system utility that transfers volumes of data over virtual terminal access method (VTAM) communication links between mainframe computers. VTAM is a standard mainframe terminal and network access communication link that is available from International Business Machine, Incorporated (IBM).
NDM, however, has several disadvantages. First, a major disadvantage of NDM is that it requires the target system to be configured prior to migrating the data. It also requires that data be moved on a dataset-by-dataset basis, rather than by moving entire volumes. This requires extensive manual support. Also, NDM requires that a new node identifier be established for the target system, since it will route the data based on the source and target systems"" node identifiers. This prohibits a company from keeping old data center identifiers intact.
The present invention solves the problems described above by using a Symmetrix Remote Data Facility (SRDF) unit designed by EMC Corporation to perform data center migrations directly from a source DASD to a target DASD. EMC designed the SRDF unit to mirror data from a primary data center to a remote, target data center, thereby providing data redundancy for the purpose of real time disaster relief, or process recovery if the primary data center experiences an outage. Under this original design, the target data center is only brought xe2x80x98on-linexe2x80x99 if the primary data center experiences such an outage or goes xe2x80x98off-line.xe2x80x99
The SRDF is a hardware unit connected to a Symmetrix DASD device. SRDF reads data as it is written from a source mainframe computer""s memory to a source DASD unit. It then transfers this data from the source DASD over ESCON or DS-3 Data Link trunks to a second, target DASD unit, where the data is written for permanent storage. The target DASD is connected to a target mainframe computer system. This data transfer allows for data on the target DASD to mirror data on the source DASD unit, thereby providing data redundancy. As the source mainframe writes new data to the source DASD, it is automatically mirrored to the target DASD.
The benefit of using SRDF is that it is host transparent. Applications are mirrored from one data center to another while application processing continues. No additional host software is required for the mirroring process. The EMC SRDF units themselves manage all the data mirroring functions. Upon deactivating the applications on the source mainframe, they can be brought up on the target mainframe within a number of hours.
The conventional operation of SRDF, however, requires that data first be entered into the source mainframe system""s memory prior to being written to the source DASD. Therefore, there is a time lag between when data is entered by the user, and when that data is mirrored on the target DASD. This time lag introduces an exposure when migrating data. At some point in time, use of an application must be cut over from the source mainframe to the target mainframe. Any data that is caught between the source mainframe""s memory and the source DASD when this cutover occurs is not reflected on the target DASD.
The present invention, identified as a Data Center Migration Method and System Using Data Mirroring, uses the EMC""s SRDF unit in a completely unique manner as defined by specific procedures. It migrates all system and application data from a primary data center to a remote target data center. Specific procedures are required to ensure data integrity is maintained and that all user updates made during the migration in the primary data center are reflected in the target data center.
Accordingly, no tapes or tape drive resources are necessary to utilize the present invention. This poses an advantage over both the Tape Backup and Ship method, and the Tape Drive Channel Extension method, in which thousands of tapes may be required.
It is another advantage of the present invention that application downtime is greatly reduced from traditional methods. Since no backup to tape, transportation, or restore to target system is needed, customer applications are down only for a sixty (60) minute window in which processing is transferred from one data center to another. Table 3 below compares total hours needed for data migration, as a function of gigabytes, among the first two traditional methods and the present invention:
It is another advantage of the present invention that since tape backup, transportation, and restore processes are not needed, the costs of resources for these processes are eliminated.
It is another advantage of the present invention that data integrity is increased for several reasons. First, no tape backups or restores are needed, thus eliminating the exposures of data corruption, missing tapes, and out-of-sequence tapes. Second, no intermediate devices, such as tape drives or channel extenders, are needed. Data is transferred directly from the source DASD to the target DASD. This eliminates another exposure to data corruption. Finally, less manual intervention is needed than with the other methods. This minimizes the exposure to data corruption imposed by human error.
An advantage that the present invention has over the Physically Moving DASD Units method, in addition to greatly reduced application downtime, is that no exposure to physical damage is incurred.
An advantage that the present invention has over NDM is that it does not require prior configuration of the target mainframe. All system configuration and operating system data is migrated with data mirroring method of the present invention. Therefore, the target system does not require a new node identifier. The old data center identifier is migrated along with the data. In addition, the present invention moves entire volumes of data at once, rather than the dataset-by-dataset method required by NDM.